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The substitution of for in solid solutions leads to a systematic decrease of the unit cell volume with increasing x value due to the smaller ionic radius of replacing in the structure. The growing strain, which is introduced into the structure by this substitution, distinctly influences the equilibrium in the process of crystal growth. This leads to a strong decrease of the texture and porosity of samples prepared by melting techniques, when the Sr concentration increases. The additional non-superconducting phases, which are formed in the process of the partial decomposition of the solid solution above the peritectic temperature, are characterized by optical microscopy in polarized light and electron microanalysis. Measurements of the magnetically modulated microwave absorption (MMMA) in (x = 0.4, 0.6, 0.8) solid solutions with different porosity and grain sizes prepared by the quench and melt technique allow one to analyse the inter- and intragrain flux penetration. The MMMA hysteresis width strongly depends on the sweep range of external magnetic field. The signal is reversible for the lowest sweep range, when the surface supercurrents allow Meissner shielding. When the sweep range increases, magnetic field begins to penetrate the sample through the intergrain weak links and irreversibility of the MMMA signal appears as a consequence of intergrain pinning of Josephson vortices. On further increase of the magnetic field sweep range, MMMA hysteresis width reflects the intragrain penetration. In contrast to porous samples, where all these stages can be clearly resolved, in solid solutions with low porosity flux pinning is enhanced and the role of intergrain Josephson coupling is significantly reduced.
Document Type: Miscellaneous
Department of Inorganic Chemistry, Faculty of Natural Sciences, Comenius University, 842 15 Bratislava, Slovakia 2:
Institute of Inorganic Chemistry, Slovak Academy of Sciences, 842 36 Bratislava, Slovakia 3:
Institute of Electrical Engineering, Slovak Academy of Sciences, 842 39 Bratislava, Slovakia 4:
Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, 60-179 Poznan, Poland